Hi Sönke, On Fri, Jan 21, 2022 at 3:52 PM Sönke Huster <soenke.huster@xxxxxxxxx> wrote: > > Hi Luiz, > > On 22.01.22 00:32, Luiz Augusto von Dentz wrote: > > Hi Sönke, > > > > On Fri, Jan 21, 2022 at 3:18 PM Sönke Huster <soenke.huster@xxxxxxxxx> wrote: > >> > >> Hi Luiz, > >> > >> On 21.01.22 22:31, Luiz Augusto von Dentz wrote: > >>> Hi Sönke, > >>> > >>> On Fri, Jan 21, 2022 at 10:22 AM Sönke Huster <soenke.huster@xxxxxxxxx> wrote: > >>>> > >>>> I just noticed that just checking for handle does not work, as obviously 0x0 could also be a handle value and therefore it can't be distinguished, whether it is not set yet or it is 0x0. > >>> > >>> Yep, we should probably check its state, check for state != BT_OPEN > >>> since that is what hci_conn_add initialize the state. > >>> > >> > >> I thought there are more valid connection states for the first HCI_CONNECTION_COMPLETE event, as it also occurs e.g. after an HCI_Create_Connection command, see Core 5.3 p.2170: > >>> This event also indicates to the Host which issued the HCI_Create_Connection, HCI_Accept_- > >>> Connection_Request, or HCI_Reject_Connection_Request command, and > >>> then received an HCI_Command_Status event, if the issued command failed or > >>> was successful. > >> > >> For example in hci_conn.c hci_acl_create_connection (which triggers a HCI_Create_Connection command as far as I understand), the state of the connection is changed to BT_CONNECT or BT_CONNECT2. > >> But as I am quite new in the (Linux) Bluetooth world, I might have a wrong understanding of that. > > > > Yep, we would probably need a switch to capture which states are valid > > and which are not or we initialize the handle with something outside > > of the valid range of handles (0x0000 to 0x0EFF) so we can initialize > > it to e.g. 0xffff (using something like define HCI_CONN_HANDLE_UNSET) > > so we can really tell when it has been set or not. > > > > I think the state switch is just possible if there is no possibility > to change a connection state back into one of the accepted states. > Unless changing the state back into an accepted state includes a call > to "hci_conn_del_sysfs", as the real issue when getting a duplicate > HCI_Create_Connection event is that device_add in hci_conn_add_sysfs > is called twice for the same connection. > > There might be other issues as well in processing a duplicate event, > but as far as I can see the bugs I trigger rely on multiple calls to > device_add which lead in the long run to multiple user-after frees > or null-pointer derefs. I tried to write that up in the bugzilla report > here: https://bugzilla.kernel.org/show_bug.cgi?id=215497 > > > When using something like HCI_CONN_HANDLE_UNSET, we need to make sure > that everywhere where we receive a handle from an event and use it to > set conn->handle, it is a valid one. Otherwise a hacked / malicious > controller would just send multiple events for the invalid handle. Well that is already the case for 0x0000, so one can in fact already abuse such a thing, so yes we probably should check if the received handle is within the valid range or not. > What solution do you prefer? If you don't mind I'd like to try to > create a patch. I'd start by initializing the conn->handle to 0xffff and add checks for it later we can add checks for received handle as well. > >>>> On 21.01.22 18:36, Soenke Huster wrote: > >>>>> When a HCI_CONNECTION_COMPLETE event is received multiple times > >>>>> for the same handle, the device is registered multiple times which leads > >>>>> to memory corruptions. Therefore, consequent events for a single > >>>>> connection are ignored. > >>>>> > >>>>> The conn->state can hold different values so conn->handle is > >>>>> checked to detect whether a connection is already set up. > >>>>> > >>>>> Buglink: https://bugzilla.kernel.org/show_bug.cgi?id=215497 > >>>>> Signed-off-by: Soenke Huster <soenke.huster@xxxxxxxxx> > >>>>> --- > >>>>> This fixes the referenced bug and several use-after-free issues I discovered. > >>>>> I tagged it as RFC, as I am not 100% sure if checking the existence of the > >>>>> handle is the correct approach, but to the best of my knowledge it must be > >>>>> set for the first time in this function for valid connections of this event, > >>>>> therefore it should be fine. > >>>>> > >>>>> net/bluetooth/hci_event.c | 11 +++++++++++ > >>>>> 1 file changed, 11 insertions(+) > >>>>> > >>>>> diff --git a/net/bluetooth/hci_event.c b/net/bluetooth/hci_event.c > >>>>> index 681c623aa380..71ccb12c928d 100644 > >>>>> --- a/net/bluetooth/hci_event.c > >>>>> +++ b/net/bluetooth/hci_event.c > >>>>> @@ -3106,6 +3106,17 @@ static void hci_conn_complete_evt(struct hci_dev *hdev, void *data, > >>>>> } > >>>>> } > >>>>> > >>>>> + /* The HCI_Connection_Complete event is only sent once per connection. > >>>>> + * Processing it more than once per connection can corrupt kernel memory. > >>>>> + * > >>>>> + * As the connection handle is set here for the first time, it indicates > >>>>> + * whether the connection is already set up. > >>>>> + */ > >>>>> + if (conn->handle) { > >>>>> + bt_dev_err(hdev, "Ignoring HCI_Connection_Complete for existing connection"); > >>>>> + goto unlock; > >>>>> + } > >>>>> + > >>>>> if (!ev->status) { > >>>>> conn->handle = __le16_to_cpu(ev->handle); > >>>>> > >>> > >>> > >>> > >> > >> Best > >> Sönke > > > > > > -- Luiz Augusto von Dentz
